The invention relates to a hydraulic control switching arrangement for a control system of a hydraulic power lift. Such control system is of a type in which a control valve is controlled via control lines of a low pressure loop.
In German patent publication DE-OS No. 29 40 403 there is disclosed a control switching arrangement in which a power lift control valve controls the high pressure working section powered by a first pump. The control valve itself however, is controlled by a low pressure control section powered by a second pump.
Since the lifting cylinder of the power lift cannot be sealed with zero oil leakage, it is advantageous to include a check valve in the working pressure line from the power lift control valve to the power lift piston, which valve opens in the direction toward the power lift, and which valve is hydraulically openable at least for lowering movements of the lift piston. Such a hydraulically openable check valve, often designated a "shutoff block" in the art, is known, e.g. from German patent publication DE-OS No. 32 47 420.
Previously, the hydraulic energy for opening an hydraulically openable check valve came from a low pressure control section, and the control connections were relatively complex and required a relatively large space.